χρῶμα σῶμα

In the 1880s, scientists could finally see chromosomes under microscopes because of new synthetic dyes. When the dyes were applied, structures inside cell nuclei lit up with brilliant color. German anatomist Heinrich Waldeyer named these structures chromosomen from Greek chroma (color) and soma (body)—'color bodies.' He was describing what he actually saw: things that took up color.

The name was practical before it was profound. Waldeyer wasn't claiming these colored bodies were the seat of heredity—he was just calling them what he could observe. But observation is how science works. The chromatic property made chromosomes visible, and visibility made discovery possible.

Within thirty years of their naming, chromosomes became the center of genetics. Thomas Hunt Morgan bred fruit flies and watched eye color correlate with inheritance of a specific chromosome. It was 1910 when Morgan realized that traits were literally tied to visible structures. The colored bodies Waldeyer had named were the actual carriers of heredity.

Today we know human cells contain 46 chromosomes—23 pairs. Each chromosome contains thousands of genes made of DNA. The word chromosome is a relic of a nineteenth-century staining technique, but it persists because the connection stuck: chromosomes are color bodies, and they color everything about who you are.